Self-powered optical detector for mechanical gauge instruments

Abstract

An embodiment of the present invention includes a display device including a mechanical indicator, a reference photodetector, a measurement photodetector, and an opaque shroud. The opaque shroud is connected to the mechanical indicator to variably cover the measurement photodetector based on a position of the mechanical indicator. The opaque shroud does not cover the reference photodetector.

The invention claimed is: 
     
       1. A display device comprising:
 a mechanical indicator, 
 a reference photodetector; 
 a measurement photodetector; and 
 an opaque shroud connected to the mechanical indicator to variably cover the measurement photodetector based on a position of the mechanical indicator; the opaque shroud not covering the reference photodetector. 
 
     
     
       2. The display device of  claim 1 , further comprising:
 a faceplate displaying a scale for indicating a position of the mechanical indicator relative to a zero-scale position and full-scale position; and 
 the opaque shroud covers the measurement photodetector to an extent corresponding to the relative position of the mechanical indicator. 
 
     
     
       3. The display device of  claim 2 , wherein the reference photodetector is proximate to the measurement photodetector; and both the reference photodetector and the measurement photodetector are positioned within an opening in the faceplate. 
     
     
       4. The display device of  claim 2 , further comprising a light source directed at least partially toward the faceplate, the reference photodetector, and the measurement photodetector. 
     
     
       5. The display device of  claim 2 , further comprising:
 a measurement circuit electrically connected to the reference photodetector and to the measurement photodetector to calculate the relative position of the mechanical indicator based on an output of the reference photodetector and an output of the measurement photodetector; and 
 a wireless communication circuit connected to the measurement circuit to wirelessly communicate the calculated relative position of the mechanical indicator. 
 
     
     
       6. The display device of  claim 5 , wherein the reference photodetector and the measurement photodetector each include at least one photovoltaic cell. 
     
     
       7. The display device of  claim 6 , wherein the measurement circuit comprises:
 a first electrical energy storage device electrically connected to the reference photodetector to store energy from the reference photodetector; 
 a second electrical energy storage device electrically connected to the measurement photodetector to store energy from the measurement photodetector; and 
 a conversion circuit electrically connected to the first electrical energy storage device and to the second electrical energy storage device to calculate the relative position of the mechanical indicator based on relative quantities of energy stored in each of the first and second electrical energy storage devices. 
 
     
     
       8. The display device of  claim 7 , wherein the energy stored in the first and second electrical energy storage devices at least partially powers at least one of the measurement circuit and the wireless communication circuit. 
     
     
       9. A mechanical gauge comprising:
 a mechanical sensing element; 
 a display device linked to the mechanical sensing element, the display device comprising:
 a mechanical indicator linked to a movable portion of the mechanical sensing device, 
 a reference photodetector; 
 a measurement photodetector; and 
 an opaque shroud connected to the mechanical indicator to variably cover the measurement photodetector based on a position of the mechanical indicator, and not cover the reference photodetector. 
 
 
     
     
       10. The gauge of  claim 9 , wherein the display device further comprises:
 a faceplate displaying a scale for indicating a position of the mechanical indicator relative to zero-scale position and full-scale position; and 
 the opaque shroud covers the measurement photodetector to an extent corresponding to the relative position of the mechanical indicator. 
 
     
     
       11. The gauge of  claim 10 , wherein the mechanical sensing element is a mechanical pressure sensor and the zero-scale position corresponds to a relatively low pressure and the full-scale position corresponds to a higher pressure. 
     
     
       12. The gauge of  claim 10 , wherein the mechanical sensing element is a mechanical temperature sensor and the zero-scale position corresponds to a relatively low temperature and the full-scale position corresponds to a higher temperature. 
     
     
       13. The gauge of  claim 10 , wherein the display device further comprises:
 a measurement circuit electrically connected to the reference photodetector and to the measurement photodetector to calculate the relative position of the mechanical indicator based on an output of the reference photodetector and an output of the measurement photodetector; and 
 a wireless communication circuit connected to the measurement circuit to wirelessly communicate the calculated relative position of the mechanical indicator. 
 
     
     
       14. The gauge of  claim 13 , wherein the reference photodetector and the measurement photodetector each include at least one photovoltaic cell. 
     
     
       15. The gauge of  claim 14 , wherein the measurement circuit comprises:
 a first electrical energy storage device electrically connected to the output of the reference photodetector; 
 a second electrical energy storage device electrically connected to the output of the measurement photodetector; and 
 a conversion circuit electrically connected to the first electrical energy storage device and to the second electrical energy storage device to calculate the relative position of the mechanical indicator based on relative quantities of energy stored in each of the first and second electrical energy storage devices. 
 
     
     
       16. The gauge of  claim 15 , wherein the energy stored in the first and second electrical energy storage devices at least partially powers the measurement circuit and the wireless communication circuit. 
     
     
       17. A method for generating a wireless signal representative of a relative position of a mechanical indicator, the method comprising:
 exposing a reference photodetector to a light source; 
 exposing a measurement photodetector to the light source; 
 covering a portion of the measurement photodetector with an opaque shroud connected to the mechanical indicator such that the covered portion corresponds to a position of the mechanical indicator; 
 measuring a power output of the reference photodetector produced by exposure to the light source; 
 measuring a power output of the measurement photodetector produced by exposure of an uncovered portion of the measurement photodetector to the light source; 
 calculating the position of the mechanical indicator relative to a zero-scale position and a full-scale position based on the measured power output of the reference photodetector and the measured power output of the measurement photodetector; and 
 transmitting the calculated relative position of the mechanical indicator by wireless communication. 
 
     
     
       18. A method of  claim 17 , wherein calculating the relative position of the mechanical indicator includes:
 calculating a first power ratio by dividing the measured power output of the measurement photodetector by the measured power output of the reference photodetector; and 
 applying a scaling transfer function to the first power ratio to find the relative position of the mechanical indicator. 
 
     
     
       19. A method of  claim 17 , wherein calculating the relative position of the mechanical indicator includes:
 calculating a second power ratio by dividing a sum of the measured power output of the measurement photodetector and the measured power output of the reference photodetector by a difference between the measured power output of the measurement photodetector and the measured power output of the reference photodetector; and 
 applying a scaling transfer function to the second power ratio find the relative position of the mechanical indicator. 
 
     
     
       20. A method of  claim 17 , wherein the transmitting of the calculated relative position by wireless communication is powered at least in part by at least one of the power output of the reference photodetector and the power output of the measurement photodetector.